The present invention relates to novel lipid compositions that facilitate the intracellular delivery of biologically active (therapeutic) molecules. The present invention relates also to pharmaceutical compositions that comprise such lipid compositions, and that are useful to deliver therapeutically effective amounts of biologically active molecules into the cells of patients.
Effective therapeutic use of many types of biologically active molecules has not been achieved simply because methods are not available to cause delivery of therapeutically effective amounts of such substances into the particular cells of a patient for which treatment therewith would provide therapeutic benefit. Efficient delivery of therapeutically sufficient amounts of such molecules into cells has often proved difficult, if not impossible, since, for example, the cell membrane presents a selectively-permeable barrier. Additionally, even when biologically active molecules successfully enter targeted cells, they may be degraded directly in the cell cytoplasm or even transported to structures in the the cell, such as lysosomal compartments, specialized for degradative processes. Thus both the nature of substances that are allowed to enter cells, and the amounts thereof that ultimately arrive at targeted locations within cells, at which they can provide therapeutic benefit, are strictly limited.
Although such selectivity is generally necessary in order that proper cell function can be maintained, it comes with the disadvantage that many therapeutically valuable substances (or therapeutically effective amounts thereof) are excluded. Additionally, the complex structure, behavior, and environment presented by an intact tissue that is targeted for intracellular delivery of biologically active molecules often interfere with such delivery, in comparison with the case presented by populations of cells cultured in vitro
Examples of biologically active molecules for which effective targeting to a patients' tissues is often not achieved include: (1) numerous proteins including immunoglobin proteins, (2) polynucleotides such as genomic DNA, cDNA, or mRNA (3) antisense polynucleotides; and (4) many low molecular weight compounds, whether synthetic or naturally occurring, such as the peptide hormones and antibiotics.
One of the fundamental challenges now facing medical practicioners is that although the defective genes that are associated with numerous inherited diseases (or that represent disease risk factors, including for various cancers) have been isolated and characterized, methods to correct the disease states themselves by providing patients with normal copies of such genes (the techniques of gene therapy) are substantially lacking. Accordingly, the development of improved methods of intracellular delivery is of great medical importance.
Examples of diseases that it is hoped can be treated by gene therapy include inherited disorders such as cystic fibrosis, Gaucher's disease, Fabry's disease, and muscular dystrophy. Representative of acquired disorders that can be treated are: (1) for cancers--multiple myeloma, leukemias, melanomas, ovarian carcinoma and small cell lung cancer; (2) for cardiovascular conditions--progressive heart failure, restenosis, and hemophilias; and (3) for neurological conditions--traumatic brain injury.
Gene therapy requires successful transfection of target cells in a patient. Transfection may generally be defined as the process of introducing an expressible polynucleotide (for example a gene, a cDNA, or an MRNA patterned thereon) into a cell. Successful expression of the encoding polynucleotide leads to production in the cells of a normal protein and leads to correction of the disease state associated with the abnormal gene. Therapies based on providing such proteins directly to target cells (protein replacement therapy) are often ineffective for the reasons mentioned above.
Cystic fibrosis, a common lethal genetic disorder, is a particular example of a disease that is a target for gene therapy. The disease is caused by the presence of one or more mutations in the gene that encodes a protein known as cystic fibrosis transmembrane conductance regulator ("CFTR"), and which regulates the movement of ions (and therefore fluid) across the cell membrane of epithelial cells, including lung epithelial cells. Abnormnal ion transport in airway cells leads to abnormal mucous secretion, inflammmation and infection, tisssue damage, and eventually death.
It is widely hoped that gene therapy will provide a long lasting and predictable form of therapy for certain disease states, and it is likely the only form of therapy suitable for many inhereted diseases. There remains however a critical need to provide new lipid compositions that further faciliate entry of functional genes into cells.